1. Field of the Invention
The present invention relates to an image forming apparatus and a method of controlling the same, and more particularly to control performed by an image forming apparatus of a laser scanning type, for correcting image forming positions.
2. Description of the Related Art
In general, to form a high-quality image at high speed, an image forming apparatus performs control for correcting image forming conditions. For example, for correction of non-uniform image densities on one sheet of recording medium caused by characteristics of the image forming apparatus, it is known to control the amount of laser light during image formation (shading control).
For example, a photosensitive member (photosensitive drum) has slightly different sensitivity characteristics to laser light depending on each area exposed to laser light. The non-uniformity in sensitivity characteristics to laser light in each area causes non-uniformity in density of an image formed on one sheet of recording medium. In view of this problem, when an image is formed on one sheet of recording medium, it is conventional practice to perform control for changing the amount of laser light according to a position on the photosensitive member to thereby suppress non-uniformity in image density. When correcting the amount of laser light, an exposure position of laser light on the photosensitive member is identified, in respect of a main scan direction (direction of scanning of laser light), with reference to a horizontal synchronization signal generated by detecting deflected laser light, and in respect of a sub scan direction (direction of rotation of the photosensitive member), with reference to a result of detection of a home position mark provided on the photosensitive member. The exposure position of laser light is identified based on a clock signal output from an oscillator, and the laser light is corrected to an amount associated with the identified exposure position. Light amount control data of laser light is generated by a controller provided in a body of the image forming apparatus, and is transmitted to a beam scanning device via a data communication bus (see e.g. Japanese Patent Laid-Open Publication No. 2011-158761)
However, an image forming apparatus that performs high-speed and high-resolution image formation by increasing the number of laser beams which expose the photosensitive member has a problem that the number of data communication buses is increased. A plurality of light sources (light emitting devices) which emit laser beams are different in light emission characteristics. For this reason, light amount setting data is generated for each of the plurality of light sources. The light amount setting data is stored in a storage medium (e.g. nonvolatile memory) provided in the beam scanning device. To read out the light amount setting data from the storage medium of the beam scanning device and cause the image forming apparatus to transmit to the beam scanning device the light amount setting data in combination with the above-mentioned shading data, as the light amount control data, the number of data communication buses has to be increased. If the image forming apparatus is configured to transmit the light amount control data by serial communication, the data communication takes a lot of time.